1. Johann Wolfgang Goethe-Universität Frankfurt
Institut für Theoretische Physik
Parton Thermalization and Energy Loss in ultrarelativistic Heavy-Ion Collisions within a Parton Cascade
Zhe Xu
in collaboration with A. El, O.Fochler and C.Greiner
QM2006, Shang Hai

2. on-shell parton cascade
Motivation
fast thermalization
on-shell parton cascade
Z. Xu and C. Greiner, PRC 71, (2005)
with only pQCD gg<->gg : no thermalization except with large s (AMPT,MPC)
including pQCD gg<->ggg: thermalization, hydro. behaviour and Jet-Quenching

3. What is the correct quantity describing kinetic equilibration?
NOT the mean free path or collision rate ns
maybe nst with the transport cross section
gg -> gg
gg -> ggg
B.Müller‘s question in
Quark Matter 2005
One has to do detailed studies.

4. momentum isotropization and kinetic equilibration
Initial condition: Minijets p0=1.4 GeV

5. q(t) gives the timescale of kinetic equilibration.

6. Transport Rates
Definition:
Boltzmann equation

7. The drift term is large.

8. special case
for isotropic distribution of collision angle

10. Bremsstrahlung processes
J.F.Gunion, G.F.Bertsch, Phys. Rev. D 25, 746(1982)
LPM suppression: the formation time
Bethe-Heitler regime

12. Initial condition with Color Glass Condensate
h: [-0.05:0.05] and xt < 1.5 fm

13. Evolution of Particle Number in bottom-up scenario
Andrej El
Particle number decreases rapidly in the very first moment
No net soft gluon production at early times!

14. Jet-Quenching in a central Au Au collision at RHIC
Oliver Fochler
3~4 too much

15. elliptic flow in noncentral Au+Au collisions at RHIC:
peripheral
central

16. Summary
PQCD Bremsstrahlung gg↔ggg are essential for the thermalization.
The transport rates are quantities determining the contribution of
different processes to kinetic equilibration.
no bottom –up
large v2, but small RAA

17. Minijets p0=1.4 GeV

21. q(t)

24. Question: Why are gg<->ggg interactions
Simulation 1
Simulation 2
thermalization and
hydrodynamical behavior
NO thermalization and
free streaming
Question: Why are gg<->ggg interactions
essential for thermalization?

26. collision probability:
Stochastic algorithm
P.Danielewicz, G.F.Bertsch, Nucl. Phys. A 533, 712(1991)
A.Lang et al., J. Comp. Phys. 106, 391(1993)
cell configuration in space
for particles in D3x with momentum p1,p2,p3 ...
D3x
collision probability:

27. Initial conditions: minijets production with pt > p0
binary approximation 
for a central Au+Au collision at RHIC
at 200 AGeV using p0=2 GeV

28. Initial conditions with smaller p0

29. Kinetic and chemical equilibration
in the central region: h: [-0.5:0.5] and xt < 1.5 fm
1~2 fm/c for the kinetic equilibration
~ 4 fm/c for the chemical equilibration

30. Kinetic and chemical equilibration

31. transverse energy at y=0 in Au+Au central collision

32. Kinetic and chemical equilibration